There has conventionally been known a linear guide device for guiding a movable body of a table or the like along a fixed unit of a bed or the like, which is constituted by a track rail having a ball rolling groove, a slider having a load rolling groove opposed to the ball rolling groove, having a no load rolling path for circulating balls from one end to other end of the load rolling groove and moved along the track rail and a number of the balls rolling between the slider and the track rail while carrying a load and circulating an endless track constituted by the load rolling groove of the slider and the no load rolling path.
According to the conventional linear guide device constituted in this way, the endless track of the slider is filled with the balls and accordingly, when the slider is moved along the track rail, the balls contiguous to each other are circulated in the endless track while colliding or sliding with each other by which there poses a problem in which the balls are worn at an early stage and the life of the device is shortened.
Hence, in order to resolve such a problem, there has been proposed a linear guide device in which a ball chain aligning and holding a number of balls is integrated to the endless track (Japanese Unexamined Patent Publication No. JP-A-5-52217). As shown by FIG. 16 and FIG. 17, according to such a ball chain 100, spacers 102 are interposed among respective balls 101 contiguous to each other, the balls 101 are connected in a shape of a rosary (i.e., string of beads) by connecting the respective spacers 102 by connecting portions 103 in a strip-like shape and the balls 101 are fabricated by injection molding of flexible resin where balls 101 are arranged in a mold as cores.
The conventional ball chain 100 constituted in this way, is integrated in an endless track 105 of a slider 104 and circulated in the endless track as shown by FIG. 18, in this case, the spacers 102 are interposed among the balls 101 contiguous to each other and therefore, mutual friction or collision among the balls is prevented and wear of the balls 101 can be minimized.
However, according to such a conventional ball chain 100, one of the spacers 102 supports two of the balls 101 disposed on both sides thereof and therefore, when an angle of contact of the spacer 102 with respect to the ball 101 is changed by bending or twisting the ball chain 100, there poses a problem in which the balls 101 drop off among the spacers 102.
Accordingly, although the conventional ball chain sufficiently achieves a function as a ball retainer for preventing mutual contact of balls, a function thereof as a so-called ball case for preventing detachment of balls is not sufficient. Therefore, according to a conventional linear guide device integrated with such a ball chain, in order to completely prevent accident of detachment of balls when a slider is removed from a track rail, as shown by FIG. 19, ball retainers 107 are installed on both sides of a load rolling groove 106 of a slider 104.
However, when a ball rolling groove 109 of a track rail 108 and the load rolling groove 106 of the slider 104 are formed in the shape of a so-called circular arc comprising a single ball rolling face, the depths of the rolling grooves 106 and 109 are comparatively small relative to the radius of the ball 101 and therefore, although as shown by FIG. 19, the ball retainers 107 can be formed on the both sides of the load rolling groove 106 of the slider 104, when the ball rolling groove 109 and the load rolling groove 106 are formed in a shape of a Gothic arch, that is, in a shape where a pair of ball rolling faces are intersected with each other, as shown by FIG. 20, the depths of the rolling grooves 106 and 109 are near to the radius of the ball 101 and accordingly, it is almost impossible to install the ball retainers 107 on the both sides of the load rolling groove 106.
Therefore, in integrating a ball chain to a linear guide device having ball rolling grooves in the shape of a Gothic arch, it is necessary to ensure sufficiently the function of the ball chain for retaining the balls and it is problematic to integrate a conventional ball chain having such a weak function as it is.
Meanwhile, such a ball chain 100 is used by being circulated in an endless track and accordingly, it is preferable to make the connecting portion 103 for connecting the respective spacers 102 as thin as possible and make a sectional area thereof as small as possible to flexibly bend the ball chain 100 in the endless track.
Meanwhile, considering that the respective spacers 102 are brought into sliding contact with the balls 101, the resin material used in molding the ball chain 100 needs to be provided with lubrication performance, wear resistance and the like with respect to rolling of the balls 101 and therefore, there is a constant restriction in selecting resin for molding the ball chain 100 and mechanical strength of the mold resin per se is difficult to provide.
Therefore, according to the conventional ball chain 100, the tensile strength of the connecting portion 103 is lower and there results a problem in which the connecting portion 103 is broken between the respective spacers 102 when the ball chain is being used in an endless circulating path.